1. Field of the Invention
This invention relates to a method of purifying propylene oxide. More particularly, this invention is concerned with the production of quality propylene oxide product which is capable of being commercially employed as an intermediate for the production of polyether polyols which are employed in the preparation of high resilient flexible polyurethane foams which exhibit high rise and are substantially free of blow hole formation.
Propylene oxide is a valuable precursor for the preparation of polyether polyols which are employable in the production of flexible polyurethane foams by reaction with a polyisocyanate in the presence of a blowing agent. In general, commercially available propylene oxide for this purpose is of high purity, substantially all impurities having been removed prior to commercial availability by subjecting the propylene oxide product to various purification techniques involving distillation and/or separation from other components produced in its preparatory reaction or introduced in purification of the propylene oxide product itself.
2. Description of the Prior Art
Techniques disclosed in the prior art involving purification and/or separation of propylene oxide are extensive. Hence, Jubin U.S. Pat. No. 3,464,897 discloses distillation of propylene oxide admixed with hydrocarbon contaminants in the presence of an open chain or cyclic paraffin containing of from 8 to 12 carbon atoms. Schmidt et al, U.S. Pat. No. 3,843,488 discloses the purification of propylene oxide by fractionation in the presence of a hydrocarbon having of from 8 to 20 carbon atoms. Biola et al Ger Offen. DE No. 2,505,664 discloses the separation of propylene oxide from a reaction mixture in the oxidation of propylene with oxidants. Washall U.S. Pat. No. 3,578,568 discloses the purification of monoepoxides by extractive distillation with ethylene glycol or certain ethers thereof. Ger Offen. DE No. 2,810,662 dated Sept. 13, 1979, discloses the purification of epoxides in a countercurrent extractive distillation process by introduction of an amine-containing compound. Schmidt U.S. Pat. No. 3,881,996 discloses a process for the recovery of propylene oxide in a high state of purity by a series of distillation steps to remove certain aldehydes and other high boiling materials Jubin, U.S. Pat. No. 3,607,669 discloses a method of separating propylene oxide from water by distilling the mixture in the presence of an open chain or cyclic paraffin containing of from 8 to 12 carbon atoms. Although a number of the aforementioned purification or separation techniques, employed alone or in combination, have been successful in the production of commercially acceptable propylene oxide products, it was noted that certain high resilient flexible polyurethane foams based on polyether polyols derived from such commercially available propylene oxide composition would sometimes collapse even though the raw materials employed in the production of such polyurethane foam product, including intermediates therefor, would meet acceptable specifications. Further investigation led to the conclusion that the foam collapse was attributable to the presence of certain nonvolatile impurities present in the propylene oxide starting material employed in the preparation of the polyether polyol. Hence, even after the obtainment of a desired propylene oxide product meeting commercially acceptable specifications, for example by subjecting the crude propylene oxide product to a series of separation and purification techniques, as aforementioned, the ultimate commercial acceptability of the propylene oxide product in the preparation of high resilient flexible foams polyurethane via polyether polyol was unpredictable due to the presence of certain unidentifiable nonvolatile impurities which led to low foam rise and substantial blow hole formation.